Administrator Guide

Table Of Contents
Figure 135. Enhanced VLT
Configure Virtual Link Trunking
VLT requires that you enable the feature and then configure the same VLT domain, backup link, and VLT interconnect on both
peer switches.
Important Points to Remember
You cannot enable stacking simultaneously with VLT. If you enable both at the same time, unexpected behavior can occur.
VLT port channel interfaces must be switch ports.
If you include RSTP on the system, configure it before VLT. Refer to Configure Rapid Spanning Tree.
If you include PVST on the system, configure it before VLT.
Dell EMC Networking strongly recommends that the VLTi (VLT interconnect) be a static LAG and that you disable LACP on
the VLTi.
Ensure that the spanning tree root bridge is at the Aggregation layer. Refer to RSTP and VLT for guidelines to avoid traffic
loss, if you enable RSTP on the VLT device.
If you reboot both VLT peers in BMP mode with static VLT LAGs, the DHCP server reply to the DHCP discover offer may
not be forwarded by the ToR to the correct node. To avoid this issue, configure the VLT LAGs to the ToR and the ToR port
channel to the VLT peers with LACP.
If supported by the ToR, enable the lacp-ungroup feature on the ToR using the lacp ungroup member-independent
port-channel command. If the lacp-ungroup feature is not supported on the ToR, reboot the VLT peers one at a time.
After rebooting, verify that VLTi (ICL) is active before attempting DHCP connectivity.
When a VLAN is created on VLTi peers, the VLTi port-channel is added automatically to the VLAN, whether the vlan
have members or not. A VLAN creation or deletion message from the VLT peer is the trigger for adding or removing
VLTi port-channels to or from a VLAN. You can manually add or remove a VLTi port-channel to a VLAN. In case a VLTi
port-channel is manually removed from a VLAN, it is added back to the VLAN after reload of the VLTi peers.
Use the lacp ungroup member-independent command only if the system connects to nodes using bare metal
provisioning (BMP) to upgrade or boot from the network. Otherwise, when the member links flap, the links become
independent switch ports and forward the traffic even before LACP is formed on that port.
Ensure that you configure all port channels as hybrid ports and as untagged members of a VLAN where the LACP ungroup
option is applicable.
BMP uses untagged dynamic host configuration protocol (DHCP) packets to communicate with the DHCP server.
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Virtual Link Trunking (VLT)